In the last decade, inspired by the success of commercial microfinance, the concept of applying the practice of equity investing to the delivery of high social impact interventions has drawn increasing attention in development circles, business academia and practitioners. In the field, impact investing funds have been raised and are being deployed, pioneering what may become a new industry, or at least a new niche in the area of risk capital investment. As is characteristic of early stages, the current definition of impact investing is as varied as the types of providers and the deployers of capital. While positive social impact is a common objective, the definition of financial success stretches from a nominal return of capital to superior commercial returns. The field calls for the formulation of analytical frameworks to better understand the various approaches, the relevant metrics for the social returns resulting from the deployment of capital, and the link between social impact and profitability.